The present invention relates to a magnetic recording and reproducing apparatus, particularly for recording and reproducing video signals and audio signals on helical tracks with a rotary magnetic head.
Rotary head type VCRs include arrangements for recording and reproducing video signals and audio signals to/from tracks of magnetic tape. An example of a typical tape format is shown in FIG. 2. Video tracks 34 for recording video signals and audio tracks 35 for recording digital audio signals, both forming helical tracks 33, are provided on a magnetic tape 30 which normally travels in the direction of an arrow 31.
A rotary magnetic head scans tracks 33 in the direction indicated by an arrow 32. TCI (Time Compressed Integration) signals are recorded as video signals on the video track 34, and PCM (Pulse Code Modulation) signals are recorded as digital audio signals on the audio tracks 35. To record the digital audio signals, original input analog audio signals are first digitalized (PCM). The PCM signals are process interleaved, and error correction words are inserted. The resulting signals are modulated, and synchronous words are inserted. Then after these processes, the audio signals are recorded on the audio track 35 of the magnetic tape 30.
FIG. 9 shows a block diagram of a conventional reproducing apparatus for reproducing digital audio signals. Signals on the audio tracks are sensed by a magnetic head 1 and are supplied to an amplifier 3 through a rotary transformer 2. The frequency characteristics of the amplified signals from magnetic head 1 through the magnetic tape are compensated by an equalizer 4, and the reproduced signals are detected by a decision circuit 5 responsive to a bit clock signal f.sub.1 supplied from a clock regenerator 7. This bit clock signal f.sub.1 is generated using the output signal of the equalizer 4 and a gate signal 10 of a servo circuit 9. After these processes the reproduced audio signals are input to a synchronous circuit 22. To establish synchronization, the synchronous circuit 22 detects the inserted synchronous words recorded on the audio tracks and cancels undesired synchronous words which are generated by bit errors. Finally, the digital audio signals are separated into the synchronous words, audio data and bit clock signals.
During operation of any VCR apparatus, the magnetic head (recording head, reproducing head) becomes worn. With the prior art apparatus, this reduces the interchangeability with other VCR apparatus, because it causes equalizing errors. As a result, the bit clock signal f.sub.1 regenerated by the clock regenerator 7 experiences time base errors called "jitter", which cause errors or problems in the operation of the apparatus.
Moreover in detecting signals from the decision circuit 5, the synchronous circuit 22 driven by a high frequency (48.6 MHz), such as an ECL (Emittor-Coupled Logic) device, is used. However an ECL device dissipates a large amount of power when the bit rate of the digital audio signals is more than about 50 Mbps (bit per second). Due to the high driving frequency, a CMOS (Complementary Metal-Oxide Semiconductor) IC that operates at a low speed, and is lower in cost, cannot be used.